S209: TARGETING THE SRC HOMOLOGY 2 DOMAIN-CONTAINING PHOSPHATASE SHP2 ENHANCES THE THERAPEUTIC EFFICACY OF JAK INHIBITION IN MYELOPROLIFERATIVE NEOPLASMS
Authors: Sarah Jungius, Sara Mattei, Simona Stivala, Jakub Szybinski, Lenka Vokalova, Alicia Rovó, Anne Angelillo-Scherrer, Stefan Dirnhofer, Sara Meyer
Journal: HemaSphere (2023)

Background: Myeloproliferative neoplasms (MPN) are hematologic malignancies that present with excessive production of mature myeloid blood cells. MPN are characterized by somatic mutations in JAK2, CALR or MPL, which result in constitutive activation of JAK2 signaling including STAT3/5, MAPK and PI3K/Akt pathways. JAK2 inhibitors like ruxolitinib effectively inhibit the JAK-STAT axis, but signaling via the MAPK pathway remains activated in vivo, thus limiting therapeutic effects. SHP2, Gab1 and Grb2 have been implicated in the signal transduction from JAK2 to the MAPK pathway, but the molecular connection is not fully clarified. Due to its important function in hematopoiesis, SHP2 is of special interest in an MPN setting. Aims: We study the role of the protein tyrosine phosphatase SHP2 in activating the MAPK pathway in MPN and evaluate its translational potential as a therapeutic target. Methods: SHP2 was depleted by shRNA in Ba/F3 cells stably expressing Jak2V617F or wildtype Jak2 along with EPOR. Pharmacologic targeting by SHP2 inhibitors TNO155 or IACS-13909 as well as dual SHP2/JAK2 targeting was evaluated in MPN cell lines and primary MPN patient cells. Corrective effects were characterized in vivo by targeting SHP2 in a Jak2V617F mutant transgenic MPN mouse model presenting with a polycythemia vera phenotype and in a MPLW515L mutant retroviral transplant mouse model with a myelofibrosis phenotype. Results: SHP2 was expressed at substantial mRNA and protein levels in MPN cell lines along with MAPK pathway activation. shRNA-induced SHP2 depletion reduced activation of MAPK pathway kinases including ERK1/2 and RSK as well as expression of MAPK downstream effectors such as DUSP6. Pharmacologic SHP2 inhibition with TNO155 or IACS-13909 was similarly able to interfere with MAPK pathway activation as shown by reduced pERK1/2 and pRSK. Of note, signaling effects were most pronounced after combined JAK2/SHP2 inhibitor exposure (A). Both SHP2 knock-down and pharmacologic targeting sensitized MPN cells to JAK2 inhibition with ruxolitinib, as reflected by inhibited proliferation at significantly lower IC50 compared to ruxolitinib as single agent (B). More moderate inhibition of proliferation was observed in Ba/F3 cells expressing wild-type JAK2 (C). In a Jak2V617F mutant MPN mouse model, SHP2 inhibition by TNO155 promptly mediated corrective effects on the MPN phenotype including splenomegaly, erythrocytosis and leukocytosis. Of note, TNO155 as single agent showed similar effects as ruxolitinib, while combined JAK2/SHP2 inhibition enhanced efficacy and was tolerable (D). In a MPLW515L mutant MPN mouse model with extensive splenomegaly and leukocytosis, combined JAK2/SHP2 inhibition promptly normalized leukocyte counts, which is not seen to this extent with ruxolitinib (E). Similarly, MPN infiltration of the spleen and extramedullary hematopoiesis in the liver was markedly reduced after one week of combination treatment. Importantly, myelo-erythroid colony formation from primary MPN patient cells was more effectively suppressed by combined JAK2/SHP2 inhibition as compared to JAK2 inhibitor single agent exposure. Summary/Conclusion: Our findings suggest a relevant role of SHP2 in MPN given enhanced MAPK pathway suppression and corrective effects when SHP2 is targeted in MPN cells, mouse models and primary patient isolates. Further studies will delineate the involvement of SHP2 phosphatase vs. non-phosphatase functions and detail the potential of JAK2/SHP2 inhibition as therapeutic approach in MPN.Keywords: SHP-2, Ruxolitinib, Myeloid malignancies